1. Field of the Invention
The present invention relates to a method and apparatus for controlling a plurality of motors for reciprocating needles, included in a knitting machine.
2. Prior Art
A knitting machine having a plurality of needles is provided with motors, such as linear motors, servo-motors or stepping motors, respectively for the needles. One motor controller for a knitting machine provided with a plurality of motors, is proposed in Japanese Patent Application Disclosure No. 3-74192. The controller is provided with a multiple input/output chip having a signal generating unit and an up/down counter for each motor, and a microprocessor having a command unit and a control processing unit.
In this prior art motor controller, each up/down counter of the multiple input/output chip calculates a position of each corresponding motor, and each signal generating unit of the multiple input/output chip gives a pulse width modulating signal (PWM signal) for varying pulse width according to a duty factor such as duty cycle determined by the control processing unit of the microprocessor to the corresponding motor driving unit. The control processing unit of the microcomputer calculates a duty factor by using a position command pulse signal provided by the command unit, and a count counted by each up/down counter (the current positions of the needle and the motor) and gives the calculated duty factor to the multiple input/output chip.
The foregoing prior art, however, takes nothing into consideration about a method of calculating a position command by the command unit of the microcomputer. If position commands for the plurality of motors are calculated sequentially and repeatedly by the common microcomputer, a long time is necessary for one calculation cycle for calculating position commands for all the motors, i.e., tens or hundreds of motors and, consequently, control speed is reduced such that the calculation is unable to be synchronized with the movement of the yarn feeder. Therefore, in the prior art, the one controller is able to control only a small number of motors.
Accordingly, it is an object of the present invention to reduce the storage capacity of a storage device storing control data for controlling a plurality of motors and to achieve the control of a plurality of needle driving motors in quick response synchronous with the travel of a yarn feeder.